1. Field of the Invention
The present invention relates to a toner which is used for developing a latent electrostatic image in electrophotographic copiers, laser printers, facsimiles and so forth and is suitable for forming a color image, and also relates to a developer and an image forming method each using the toner.
2. Description of the Related Art
In electrographic color image forming apparatuses, in order to yield an image density (ID; reflection density of a toner image on a sheet of paper) of 1.2 with each of monochrome color images of cyan (C), magenta (M), and yellow (Y), conventionally a toner adhesion amount (adhesion amount of a toner on a unit area of a recording medium) of 0.4 mg/cm2 (4.0 g/m2) or more has been required.
In recent years, it has been requested to solve environmental problems in many fields of industry, however, it has been difficult to reduce toner adhesion amounts in the electrographic industry, leaving such environmental problems unsolved.
Furthermore in development of toner, there are some cases in which a pigment is used at a high concentration (11% by mass to 20% by mass) to the total amount of toner. In such cases, the image density (ID) can be increased. However the simple body of pigment is expensive, the toner price is raised because of high concentration of pigment used in the toner. In addition, the use of pigment at high concentration decreases image sharpness.
On the other hand, commercially available conventional toners have a volume average particle diameter of 5.1 μm at the minimum, and therefore, have been insufficient for satisfying today's demands for obtaining high resolution images and highly fine images. The quality of images produced by using any of commercially available conventional toners is still insufficient as compared to the quality of images produced by offset lithography. Images produced using any of commercially available conventional toners are also inferior in color reproduction ranges to images produced by offset lithography.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2006-145703 describes that an optical reflection density (ID) of 1.3 is yielded with an adhesion amount of yellow toner of 0.1 mg/cm2 to 0.5 mg/cm2, using C. I. Pigment Yellow (PY) 185. However, in the Examples of JP-A No. 2006-145703, it is described that the toner adhesion amount with which an image density (ID) of 1.3 measured by X-RITE reflection densitometer (manufactured by X-Rite Co.) is yielded is 0.32 mg/cm2 at the minimum. Based upon the results of the Examples, the adhesion amount of yellow toner at which an image density (ID) reaches 1.2 becomes 0.30 mg/cm2, when converted into a relationship between image density data that has been accumulated in the past and adhesion amounts of toner. The adhesion amount of toner still remains large.
In JP-A No. 2005-352128, optical density is measured based upon light transmittance instead of light reflectance. It is known to those skilled in the art that the difference between the reflection density and transmission density is not so significant that it would affect comparative results in optical density. In the Examples of the above application, ID of 1.07 for cyan, 1.06 for magenta, and 1.06 for yellow at the maximum were yielded, with a toner adhesion amount of 0.4 mg/cm2 [=4.0 g/m2]. The adhesion amount of toner still remains large.
Also in Japanese Patent (JP-B) No. 3778193, the optical density has been measured using light transmittance instead of light reflectance, however as mentioned above the difference between the optical density measured using light transmittance and the optical density measured using light reflectance is not significant. In the Examples of the above specification, ID of 1.38 for cyan, 1.29 for magenta, and 1.24 for yellow at the maximum were yielded with a toner adhesion amount of 0.35 mg/cm2. These correspond to toner adhesion amounts of 0.30 mg/cm2 for cyan, 0.32 mg/cm2 for magenta, and 0.34 mg/cm2 for yellow, for an image density (ID) of 1.2 to be yielded, which are calculated in the same manner as described above by calculation. The toner adhesion amounts of the Examples of the above specification are still large. In addition, in 3C, 3M, and 3Y in the Examples of the above specification, the amount of each pigment added was 11% by mass, which is high and thus has the same problem as described above.
Furthermore, JP-A No. 2001-324835 discloses a yellow toner which exhibits a reflectance of 15% or less to light having a wavelength of 440 nm to 460 nm and a reflectance of 50% or more to light having a wavelength of 500 nm, and discloses spectral reflectivities of toners in the Examples. When a reflection density (ID) to the spectral range of 400 nm to 700 nm is calculated based on the spectral reflectivities, the ID is 0.32. The reflection density (ID) is 0.37 in an example cited as known example. The toner adhesion amount is 0.4 mg/cm2, and thus remains large. In Examples 1 to 6 and 8, the toner adhesion amount still remains large. In Example 7 the amount of pigment added is large constituting a problem similar to that described above.
In JP-A No. 11-167226, the reflection density is measured using a status-A filter, which is an International Standard for color density measurement and different from a status-I filter used in density measurement of color images in common electrography. The reflection density measured by using the status-A filter is slightly different from the reflection density measured by using the status-I filter, however the difference causes no problem when the resulting reflection densities are compared. In Example 2, with a toner adhesion amount of 0.1 mg/cm2 [=1 g/m2], densities, which were measured by using a status-A filter, of 1.26 for cyan, 1.22 for magenta, and 1.25 for yellow were yielded. The amount of pigment added was 15% by mass, which is a problem similar to that mentioned above.
Thus, at present, it has been desired to promptly provide a toner which achieves a sufficient image density with a normal addition amount of pigment, without the necessity of adding a large amount of pigment, even with a low toner adhesion amount, and decreases a toner consumption rate to thereby contribute to solution to environmental problems, and achieves a high quality image, and can enlarge the color reproduction range, and provide related technologies.